Electric blasting initiator



940. s. HANDFORTH ET AL 2,212,118

ELECTRIC BLASTING INITIATOR Filed April 20, 1939 flan/9y Lf/anaforf Ch RC1]; INVENTORS 79- 4 61752505. 15215 32 I? A TJ'ORNEY the juncture.

Patented Aug. 20, 1940 UNITED STATES PATENT OFFiC ELECTRIC BLASTING INITIANR Application April 20, 1939, Serial No. 268,892

5 Claims.

The present invention relates'to -a new and improved electric blasting initiator.

As is well known, the electric blasting initiators in use heretofore have contained a hard plug of sulfurous material for the purpose of holding the leg wires in place. This wire-containing plug is surmounted in the charged initiator shell by a superimposed layer of viscous water-proofing material. On top of this waterproofing layer. is a final seal of sulfurous material.

The assembly described has many -defects and disadvantages. Such an assembly requires a shell of great length. When delay trains are employed the length of theshell is sometimes longer than the conventional copper alloys can be drawnwith convenience.

Furthermore in forming the sulfurous composition seal, molten material must be poured by hand into a loaded shell. hazards thus involved, considerable technique is required to assemble such an initiator properly and to introduce the water-prooflng composition so that the latter does not enter the explosive charge but holds the wires in proper'position and seals the cap against moisture.

Even when such an initiator is assembled in the best possible manner without accident, this type of closure cannot be relied upon to furnish a lasting water-proof, moisture-proof seal. Under the conditions of hot and cold storage which the initiator must undergo, contraction of the sulfur seal on cooling, or the cracking of the same, permits escape of the water-proofing composition and entrance of water or moisture.

We are aware that many attempts have been -made to overcome these diillculties, and that various structures have been proposed with this end in view. Yet none of these previous proposals have proved operable in the field. For instance, it has been proposed to thread the leg wires through a single bore in a preformed rubber plug with the application of cementitious means at Unfortunately this type of. initiator assembly likewise was not satisfactory and was not sumciently waterand moisture-resistant for wet work.

Accordingly, the sulfur sealed initiator with viscous, water-proofing layer and sulfurous plug has remained the only type of electric blasting initiator relied upon in the iield prior to the present invention, in spite of the frequent com V plaints arising therefrom. Of the many proposalsforreplacing the same, none have proved to be satisfactory under conditions encountered In addition to the in the field.

The object of the present invention electric blasting initiator of simplified design having improved resistance to water and moisture. A further object is a method of manufacturing said initiators which eliminates the hazardous step of pouring molten materials into the charged shell. An additional object is an electric blasting initiator adapted to mechanical assembly. Another object is such an initiator which is shorter in length.

Additional objects will be apparent from the 7 following detailed description of 'our invention.

We have found that the foregoing objects are accomplished and the disadvantages overcome by forming a plug of resilient material about and in conjunction with each of the spaced leg wires to provide a water-proof and moisture-resistant seal between plug and wires. The charged shell is then crimped into place about the resilient plug to form a similar water-proof and moistureproof seal between plug and shell wall.

In forming this tight crimp we prefer to employ the uniform bead type such as that formed by the device disclosed and claimed in copendi'ng application Serial No. 181,646, filed December 24, 1937.

position, molded and vulcanized in place about the spaced leg wires, but any material possessing similar resilient properties may be employed. For,

It should be noted that highly satisfactory initiators from the standpoint of water resistance have been produced by us by employing finished plugs exhibiting elasticity or resiliency of the general-order of magnitude such as that determined by a measurement in'the neighborhood of 90 on a standard durometer of type "A furnished by the Shore Instrument Company. We have found that it is undesirable to have the finished plug too elastic, for the reason that if; it is too soft it will not hold *a crimp satisfactorily with respect to water resistance and the like. Furthermore, if the plug hardness gets below a certain limit the-molding operation is complicated by the fact that the plug material adheres to the mold in the curing operation. In this connection we have found it to be undesirable to employ material curing toa point any softer than that determined by ,a measurement of 30 is an on the durometer, described in the foregoing.

The resilient plug is preferably of rubber comtion.

no adhesion present. The strength of the plug, determined by pulling one wire out of the assembled cap, was 7.8 pounds, and the results of a '70 pound ice water test for 24 hours were good.

We have determined, also, that highly satisfactory initiators were prepared without molding difficulties by controlling the plasticity of the rubber stock to be vulcanized. In particular we greatly prefer to employ rubber stock exhibiting a plasticity between and 200 as measured on the Williams plastometer.

The plug may be of any convenient shape and size so long as it is formed in place about the leg wires. The electric blasting cap assembly according to our invention may be more readily understood by referring to the various figures of the drawing. These are for the purpose of illustration only and the scope of our invention is not to be limited thereby. Like numerals designate corresponding parts throughout the various figures.

Figure 1 is a view in cross-section of the improved electric blasting initiator of our inven- Figure 2 is an enlarged view of the resilient plug formed about the leg wires. plan view of the lower portion of a two-piece mold, for forming the resilient plugs of our invention. Figure 4 is an end view of the two portions of the mold.

Referring in detail to the-various figures, in Figure 1, the numeral l designates a metal shell into which the resilient plug 2 formed about leg wires 3, is crimped with uniform beads at 4 to form a moisture-proof, water-resistant closure. The insulation 5 on the leg wires preferably terminates within the body of the plug as shown at 6 in Figure 2. The conductors in the bridge plug type of cap terminate in the bridge posts I supporting the bridge wire 8. At the lower end of the shell is the charged portion 9' loaded in conventional fashion with any convenient number of charges. Although this embodiment shows the preferred bridge plug type of assembly, it should be noted that my invention is not limited thereto, but may be employed with the match head assembly and any other conventional types.

One method of forming the plugs about the wires, is to place plug material about, the leg wires in the lower portion IU of the mold shown in Figure 3. The leg wires are threaded through the entries H and passed on through the mold cavity 82, the'ends of the wires being held in place by the centering guides l3. Then the top portion of the mold Ill-a. having complementary depressions is brought down and the plug mate-I rial is molded about the wires to form a cylindrical plug. The relation between these two portions of the mold is shown in Figure 4, which is an end view thereof, including the guide posts I! for properly aligning the two sections. The numeral 55 designates the heating fluid supply entry for heating the mold, while I6 is the exit for the same. After the molding step and any required vulcanizing period is completed, the finished plugs may be crimped .in place in the charged shell, to give a water-proof, moistureproof assembly.

The following example will serve to illustrate in greaterdetail a preferred embodiment of our invention. It is to be understood that this is for the purposeoi illustration only and does not limit thescope of the invention. p f

Figure 3 is a Plugs testing at 30 were satisfactory. There was Example A rubber composition was formulated as follows:

Parts The resulting composition was formed into strips. The leg wires for the electric blasting initiators were then passed in pairs through the cavities in the bottom portion of the mold as described in the foregoing. The end of each leg wire was stripped so that the insulation terminated somewhere Within the mold cavity through which the wire was threaded. A strip of the uncured rub-- ber prepared according to the above formula was placed across the various mold cavities beneath the leg wires. Another strip was placed above said leg wires. The mold was then -closed by putting it in a press and compressing the two portions together. The mold was then maintained at a temperature of approximately 305 F. for a period of approximately two minutes, at the end of which time the rubber plugs cured in place about said leg wires, were removed and inspected for defects. The plugs were then crimped into place in charged initiator shells. They were then tested for water resistance and ability to withstand a pull on the leg wires.

In the water test these finished electric blasting initiators were subjected to ice water under 70 pounds pressure for a period of 24 hours. They were then taken out and fired over lead plates without any failures occurring.

The pull test was conducted by subjecting each of the leg wires to a 17 pound pull on a Scott tension tester of the pendulum type. The pull test results are of course dependent upon many factors such as the type of rubber stock, the molding conditions of pressure and temperature, and the dimensions of the plug and the length of strip wire within the plug. The foregoing conditions werehighly satisfactory in that all plugs passed this particular test.

An improved molding method is disclosed and claimed in copending application Serial No. 181,- 643,filed December 24, 1937.

Our novel electric blasting initiator assembly displays manifold advantages. It ishighly su'-' perior to any assembly in the prior art with respect to resistance to water and moisture. It is much more durable than the hard plug initiators of the art, and also safer, due to the resilient closure member.v It is much shorter in length and requires a shorter metal shell. A very important advantage is that it may be made without any hazardous pouring of molten liquids into the charged shell. Furthermore, it is readily adapted to mechanical assembly. These and other advantages have'rendered our initiator in great demand inthe art.

' In the foregoing we have described in detail certain specific embodiments of ourinvention. It will be understood, however, that many variations may be made without departing from the spirit and scope of the invention. For instance, although electric blasting initiators have been portrayed quite broadly as a class in the foregoing, it will be appreciated. that ourinvention is applicable to all of the various conventional species of said electric blasting initiators; for example, electric squibs, electric blasting caps, electric delay squibs and blasting caps, and initiators of the conventional bridge plug, match-head, and bridge plug bead types. While rubber composition plugs have been described as our specific embodiment, it has also been brought out that any resilient plug is included within the scope of our invention including materials such as rubber substitutes, resilient organic materials and the like. We therefore intend to be limited only by the following patent claims.

We claim:

1. An electric blasting initiator comprising a charged shell, spaced leg wires entering the mouth of said shell, a plug of rubber-like ma-- I terial of the character described formed about said spaced leg wires and disposed in a positionclosing the mouth of said shell, said leg wires extending through said plug material substantially in a straight line and substantially parallel to each other, and a crimp extending around the circumference of said shell in the region enclosing said plug forcing the shell wall into and deforming said rubber-like plug to. complete a water impervious juncture. q a

2. In an electric blasting initiator of the type including a charged shell, spaced leg wires entering the mouth of said shell, a high resistance wire completing the circuit between said leg wires within said shell, and an explosive charge in firing relationship with said high resistance wire; the closure element consisting of a plug of 35 rubber-like material of the" character described molded about and between said leg wires and disposed in a position closing the mouth of said shell, said leg wires extending through said plug material substantially in a straight line and substantially parallel to each other, and a crimp extending around the circumference of said shell in the region enclosing said plug forcing the shell wall into and deforming said rubber-like plug to complete a water impervious juncture.

3. An electric blasting initiator comprising. a charged shell, spaced leg wires entering the mouth of said shell, a plug of rubber composition of the character described molded about and between said spaced leg wires and disposed in a position closing the mouth of said shell, said rubber plug being characterized by a durometer hardness of at least 30, said leg wires extending through said plug substantially in a straight line and substantially parallel to each other, the insulation on said leg wires terminating within the body of said plug, and a crimpextending around the circumference-of .said shell in the region enclosing said plug forcing the shell wall into and deforming said rubber-like plug to complete a water impervious juncture.

4. 'The method of producing a water impervious electric blasting initiator which comprises molding a resilient readily yieldable plug of rubberlike material of the character described about and between spaced leg wires, inserting said plug in the mouth of a loaded shell, and forming a crimp around the circumference of said shell in the region enclosing said plug forcing the shell wall into anddeforming said rubber-like plug to complete a water impervious juncture.

5. An electric blasting initiator comprising-a charged shell, spaced leg wires entering. the mouth of said shell, a plug of rubber-likemateria'lof the character described formed about said spaced leg wires and disposed in-a position closing the mouth of said shell, and a crimp extending around the circumference of said shell in the region enclosing said plug forcing the shell wall into and deforming said rubberlike plug to complete a water impervious juncture.-

STANLEY L., HANDFORTH. CHARLES R. JOHNSON. GILBERT H. s rrH.

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